Identification of hydrogeochemical processes affecting the hydrochemistry of groundwater: A review

Hydrogeochemical processes are the processes that bring seasonal and spatial fluctuations in groundwater chemistry.These include rock-water interactions, ion exchange, evaporation, and other natural processes that affect groundwater as it flows from one location to another or as it remains at one location.Numerous ionic ratios, scatter plots, and diagrams are available for the identification of these processes.Ion exchange is an important contributor to groundwater chemistry and is of two types: direct ion exchange and reverse ion exchange.Rock-water interaction is another significant mechanism because the mineral content and formation of rocks through which groundwater flows, will influence its chemical composition.There are two major natural weathering processes, involving carbonic acid and sulphuric acid as the weathering agents.The ratios of Ca: HCO 3 and Ca: SO 4 help to identify the type of carbonate mineral being dissolved by these two acids.Groundwater chemistry is also impacted by anthropogenic factors like mining activities and improper disposal of industrial and sewage waste that can increase the concentration of nitrate and several heavy metals in it.The concentration of ions present in groundwater can be used to categorize it into different hydrogeochemical facies using Piper and Chadha diagrams.Identification of these hydrogeochemical processes helps to figure out the primary source of contamination of groundwater.We have tried to compile the information in one document.These processes provide an idea about mineral composition and hence the hydrogeology of the area.However, no single approach can reliably identify a certain process, we require a combination of indicators for this, that can help to develop different hydrogeochemical models for the prediction of groundwater quality.